The art of preventing or reducing the occurrence of disease caused by bacteria and other organisms which are ingested into the alimentary canal of human beings is well developed, and the toxic effects of certain metal ions carried in suspension in water are known in this connection.
Whilst there has been considerable investigation into the germicidal properties of electrolised silver ions carried in suspension in water, such investigation has been directed towards the development of systems for purifying drinking water, or water that is otherwise likely to be ingested into the human stomach, e.g. swimming pool water. Thus, work done so far has concentrated on the effects of silver ions on coliform bacteria concentrations which arise from faecal contamination of water.
Our researches have established that silver ions carried in suspension in water in appropriate concentrations are effective to kill or otherwise render innocuous bacteria and other organisms that cause respiratory diseases in human beings. Such bacteria include, inter alia, those known as Legionella Pneumophila, and their relatives, which bacteria cause the newly-recognised respiratory disease known as Legionaires Disease.
That disease of the human body is particularly hazardous to elderly people, and to sick people, and is caused by the penetration of the bacteria, Legionnaire Pneumophila, deep within the passageways of the human lungs, into the alveoli, where they multiply, and also gain access to the bloodstream via the fine blood vessels that line the walls of the alveoli for the purpose of receiving oxygen from air breathed into the lungs. The passageways (bronchial tubes and bronchioles) which communicate with the alveoli are lined with mucus.
We have established that the bacteria Legionella Pneumophila have the following characteristics:
(a) they survive only in a water environment; PA1 (b) they die if deprived of that environment; PA1 (c) they can be taken into the human alimentary canal and will pass therethrough without causing any harm; PA1 (d) they give rise to Legionnaire's disease by gaining access to and multiplying in the small air sacs (alveoli) in the lungs, in which sacs the normal process of oxygenation of the blood occurs; PA1 (e) they can enter the human bloodstream via the blood vessels which line the alveoli, and be carried in the bloodstream to other parts of the body where they do harm; PA1 (f) they are impeded by the mucus which lines the air passages (bronchial tubes and bronchioles) which lead to the alveoli; and PA1 (g) they can enter the alveoli only by being carried in very small droplets of water (less than 10 microns in diameter) which are small enough to pass through the passages leading to the alveoli without colliding with and being absorbed into the mucus lining those passages. PA1 (a) they each incorporate a water recirculation system in which water is continuously recirculated, with the losses being made up by the admission of make-up water; PA1 (b) they each include an air exposure zone through which the circulating water passes in direct contact with atmospheric air; and PA1 (c) in that zone the water impinges on one or more solid surfaces, which surfaces may be stationary or moving, at an impact velocity that is large enough to cause small water droplets (of sizes down to three microns diameter) to be ejected from the water into the atmospheric air. PA1 (1) fountains and artificial waterfalls, both indoors and outdoors; PA1 (2) water cooling apparatus in which evaporation of the continuously recirculated water is used to provide cooling of the circulated water; and PA1 (3) air humidifying apparatus in which evaporation of the continuously recirculated water is used to humidify a flow of atmospheric air. PA1 (a) a water discharge means for discharging water into an evaporation zone through which atmospheric air may flow in contact with the water whereby to effect evaporation therefrom; PA1 (b) means for breaking up the discharging water flow whereby to increase the free surface area of the water available for evaporation; PA1 (c) means for causing a said flow of atmospheric air through said zone; PA1 (d) collection means for collecting unevaporated water exiting from said zone; PA1 (e) duct means interconnecting the collection means and the discharge means; PA1 (f) pump means connected in the duct means for returning water from the collecting means through the duct means to the discharge means; and PA1 (g) a decontaminating means connected in that part of the apparatus comprising the duct means and the discharge means for introducing into the water flowing therethrough metal ions at a release rate sufficient to produce in the flowing water a predetermined concentration of metal ions sufficient to kill preselected kinds of respiratory disease causing bacteria and other organisms present in the flowing water.
Metal ions can be conveniently introduced into water by passing it through an ionising chamber in which a pair of metal or metal alloy electrodes are spaced apart and energised by a suitable alternating or uni-directional electrical potential.
It has been found that water having silver ions so introduced in concentrations of less than one part in ten million parts of water (by wt) constitutes a lethal environment for respiratory disease causing bacteria such as Legionella Pneumophila. It has also been found that water having ions of copper or zinc so introduced in concentrations of less than one part per million parts of water (by wt) constitutes a lethal environment for photo-synthesising and other organisms which assist in the development of Legionella Pneumophila. The combined effect of the two ion types inhibits the growth of bacteria and other organisms which give rise to Pontiac and Humidifier fevers.
Respiratory diseases most frequently arise from the direct invasion of the lungs by the relevant organisms carried in inhaled breath.
Certain types of apparatus which employ water as a working fluid medium provide an advantageous environment for the multiplication of such respiratory disease causing organisms, and moreover provide a means of disseminating such organisms into the atmospheric air. Such apparatus have the following characteristics:
Such water recirculating apparatus include the following:
In such water cooling apparatus of the kind referred to at (2) above, the recirculated water also passes through a heat source whereby to extract heat therefrom. As an example, such a heat source may comprise a heat exchanger of a refrigeration unit, which unit may itself comprise part of an air conditioning plant, for example for a building. Alternatively, the heat source may comprise a steam condenser as used for example in conjunction with a steam driven electric power generation plant, the circulated water being passed through the cooling water circuit of the steam condenser.
In each of those two applications, the recirculated water absorbs heat from the heat source, and is itself cooled by evaporation in an atmospheric air flow in said air exposure zone, before being recirculated to absorb further waste heat from the heat source.
In such applications, the pipework for carrying the circulating water from the heat source to the said air exposure zone works at temperatures that are particularly conducive to the multiplication of such respiratory disease causing organisms. Such organisms thus colonise the interior of that pipework, and moreover travel with the water leaving that pipework, so that they can escape into the atmospheric air flowing in said air exposure zone.
Thus, there is a high risk that water entering the said air exposure zone will carry into it Legionella Pneumophila bacteria, and also other bacteria and organisms (such as protozoa, algae, and slime moulds--with which organisms the bacteria Legionella Pneumophila symbiotically associate) that also colonise those warm pipework parts and travel in the water leaving that pipework.
Likewise, there is a high risk that Legionnaire Pneumophila bacteria, in particular, will be emitted from such zone in water droplets that are carried away in the exiting atmospheric air flow, and that many of such droplets are of, or will evaporate down to, the aforesaid small size at which they are able to penetrate the alveoli of people who breathe in atmospheric air coming from the exit ducts of such apparatus.
Similarly, other water droplets of appropriate size may carry away from said zone other bacteria and organisms which can give rise to Pontiac fever and/or Humidifier fever in those persons who inhale those water droplets present in humidified atmospheric air leaving said zone.
In many present day water re-circulating apparatus which have been used to cool the circulating water by evaporation in the air exposure zone, reliance has been placed upon the injection of toxic chemicals (such as chlorine and its compounds, and more recently and expensively, ozone) into the circulating water in order to control and limit the growth of bacteria (and organisms which may aid their growth) and of organisms which by their clogging effect may tend to impede the operation of the overall system.
Such chemicals give rise to additional expense, and also problems in their use, since they can evaporate, degrade on contact with sunlight and organic material, and being sometimes highly reactive attack the pipework and mechanisms of the system. Such expense arises from the costs of providing the chemicals and the means for injecting them automatically, and the additional maintenance that arises from their use. If manual injection is relied upon, there is the additional hazard of infection in the event that the injection timetable is not strictly adhered to.
A further problem arises in that hazardous chemicals will be present in the bleed-off water, which may find its way into a variety of collection points from which water intended for human or animal use is obtained.
Because of the difficulties which arise from the use of toxic chemicals to prevent the growth of undesirable bacteria and other organisms, there has been a move away from the use of such evaporative water cooling systems in relation to air conditioning systems for buildings, in favour of alternative, more expensive water cooling systems in which the water to be cooled is passed through a heat exchanger which comprises an enclosed water circuit over which atmospheric air is blown so as to cool the water flowing through that circuit. In such systems the water has no opportunity to come into direct contact with the atmospheric air so that no air-borne, bacteria-carrying water droplets can be formed.
In air humidifiers of the kind referred to at (3) above, there is a similar risk of disseminating in an atmospheric air flow respiratory disease producing bacteria and other organisms carried in small water droplets. Such humidifiers may be of the kind in which evaporation takes place in water falling freely over slats or baffles, or of the kind in which a stream of water is caused to impinge on the surface of a spinning disc whereby to break up the water flow into a series of small water droplets.
The present invention seeks to provide a means for a method of reducing the infectivity of the unwanted but unavoidable small water droplets present in the output air flow of such water recirculating apparatus, which means and method do not rely on the injection of toxic chemicals to control the growth of undesirable bacteria and other organisms in the circulating water.
We are aware of a prior proposal (see U.S. Pat. No. 4,525,253--Hayes et al, published 25.6.85) to use, in a water purifying means for a swimming pool or other water reservoir, a metal ion release means for simultaneously releasing ions of silver, copper and nickel from similar, metal alloy electrodes, in an endeavour to kill coliform bacteria and render that body of water potable, the water being circulated for that purpose from the reservoir to an external purifying device and back to the reservoir solely for effecting the desired purification.